A gas turbine engine typically comprises a series of rotatable components, both in the compressor and turbine of the engine, which are housed within a casing. The rotatable components each comprise an array of blades, each having an aerofoil cross section. The blades are attached to a central hub or drum. The blades of the rotatable components accelerate the air through the engine and/or extract energy from the air. Each of the rotatable components are coupled with a static component which comprises an array of vanes that are also of aerofoil cross section. The static components are connected to the radially inner and/or outer casing components.
Typically air is bled from the compressor to provide cooling and sealing air to the turbine. Air can be bled from the compressor using one or more bleed ports. The bleed ports may be annular ports that extend circumferentially around the casing of the compressor. Alternatively, a series of discrete bleed ports may be provided circumferentially around the casing.
The use of bleed ports is important for cooling and sealing, but the provision of such holes can be a cause of aerodynamic losses.